As modern CT scanners become more sensitive, the ability of scanners to discriminate smaller and small abnormalities – such as spontaneous aneurysmal subarachnoid hemorrhage – continues to increase. This BMJ paper makes another case for forgoing lumbar puncture in patients with a negative CT scan.
Specifically, they say that all the SAH in their cohort was picked up by a 3rd generation scanner as long as the scan was performed within six hours of headache onset. Unfortunately, this is another one of those studies that uses follow-up as a proxy for the gold standard evaluation – only half of their enrolled cohort underwent lumbar puncture. They followed up their patients for six months, but survival at six months doesn’t rule out pathology, it only rules out death from that specific pathology, and only if an autopsy was performed.
But, CT scan is starting to get close to the point where the false negatives of CT are equivalent to the false positives of the lumbar puncture – and I would imagine the costs and harms to the patient begin to approach equivalence. It definitely changes the equation for your patients when you come back with a negative CT scan and your patient wants to know what the chances are they really need this lumbar puncture.
“Sensitivity of Computer Tomography Performed Within Six Hours of Headache For Diagnosis of Subarachnoid Haemorrhage: Prospective Cohort Study”
www.ncbi.nlm.nih.gov/pubmed/21768192
Just my two cents…all of the studies that have looked at this are pretty weak, and they don't study the types of patients that are pertinent for us in the ED, namely the undifferentiated headache patient. Until there are REALLY good studies to support this, LP should not be skipped. Just ask any neurosurgeon about it…don't skip the LP. The literature on this isn't even close to allowing us to skip the LP. Rob Rogers. P.S. great site by the way.
There is definitely not yet enough good evidence allowing us to skip the LP – but this is another piece of a larger trend that I at least am less disinclined to hate than utilizing CTA to find asymptomatic aneurysms. It is not beyond the realm of imagination that we are approaching the day where we identify a patient population in which x-generation noncontrast CT will be as accurate at identifying SAH as LP…and everyone who falls outside that narrow definition will need an LP. The JWatch reviewer for this article was a little less conservative in their summary.
Very interesting to read your post Dr Radecki, today now that we have the latest study by this group. As if you were looking into the future.
By the way I find your blog an absolute must to read for all interested in EM and crit care.
Lev V